First of all, head to https://melonwiki.xy...ed-installation - and download MelonLoader.Installer.exe from the section titled Automated Installation.
Once this has been downloaded, run the installer.
Next, you should see a button called SELECT (in between the label Unity Game and a box saying Please Select your Unity Game...). Click this, and browse to where you installed Car Mechanic Simulator 2021. In my case, this is E:\Games\SteamLibrary\steamapps\common\Car Mechanic Simulator 2021 - but obviously this is likely to be different for you. Select Car Mechanic Simulator 2021.exe, and click Open.
This should bring you back to the Melon Loader installer. From here, click the Install button, and the installer will set up the loader.
If everything has gone right, your Car Mechanic Simulator 2021 install folder should have the following folders added: MelonLoader, Mods and Plugins.
 
Now you should have Melon Loader installed for the game, it is time to install the mod itself. You will want to download the main file from the EZScrap downloads page - EZScrap (Melon Loader) (preferred). Once downloaded, extract the file to where you installed Car Mechanic Simulator 2021. Once this has been done, there should be 2 files inside the Mods folder in your game installation folder - EZScrap.cfg and EZScrap.dll
 
Now just launch the game like normal through Steam - first time after installing Melon Loader it will take a little longer than normal to start, but this is expected! The game should launch and EZScrap will start working once you begin using the Scrap Workbench.

You can also edit EZScrap.cfg using notepad to customize the scrap multiplier - change the number on the line with ScrapMultiplier = 10 to whatever you feel works bnest for you - eg: for a 20x multiplier change this line to ScrapMultiplier = 20
To force the maximum scrap per part, you can also enable the AlwaysBigBonus option, by changing the line AlwaysBigBonus = false to AlwaysBigBonus = true